From 626893638f8a43caf00cf5ecae74f876c9a129d7 Mon Sep 17 00:00:00 2001
From: Michael Mikonos <127171689+mknos@users.noreply.github.com>
Date: Sat, 23 Sep 2023 18:26:58 +0800
Subject: [PATCH] tac fails to read a file

* tac reads from stdin when run with no file argument
* GNU tac accepts file argument of '-' for stdin but ppt version does not
* I get an array error when reading from a file: perl tac tac

Bad read on [ARRAY(0x1a04270)]:  at tac line 197.
	IO::Tac::get_lines(IO::Tac=GLOB(0x19ef4b8)) called at tac line 150
	IO::Tac::READLINE(IO::Tac=GLOB(0x19ef4b8)) called at tac line 43

* When debugging this I found that $tell is set to zero, then in the tell()
 perldoc manual it explains that tell() doesn't work with sysopen()
* Replacing tell() with sysseek() call fixes the problem on my system
---
 bin/tac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bin/tac b/bin/tac
index 3b3aabef..5d44eb4e 100755
--- a/bin/tac
+++ b/bin/tac
@@ -191,7 +191,7 @@ sub get_lines {
         # record separator has been broken across two chunks.
         my $file = *$self->{files}[0];
         CHUNK: {
-            my $tell = tell $fh;
+            my $tell = sysseek $fh, 0, 1;
             unless ($tell > $size) {
                 sysseek $fh, 0, 0       or confess "Bad seek on [$file]: $!";
                 sysread $fh, $_, $tell  or confess "Bad read on [$file]: $!";